Looking to provide a cleaner, healthier indoor environment for the 450-plus employees at its headquarters in Scottsdale, Ariz., 1st National Bank of Arizona sought to improve air filtration to the highest efficiency possible with its existing HVAC system.

“With a simple upgrade of the HVAC filter, we were able to achieve that goal and more,” Domenick Orlando, CAFS, of Dave Downing & Associates, the indoor-air-quality (IAQ) and air-filtration consulting firm that managed the project, said.

“More” included a Clean Air Award from the National Air Filtration Association.

A GOOD FOUNDATION

The 130,000-sq-ft Class A office building already had an excellent HVAC system in place, which made implementing changes easy and cost-effective.

The central plant includes two Trane Centravac chillers and a Trane screw chiller. Chilled water is delivered to four large Temtrol air handlers in two penthouses on the roof. With close to 90,000-cfm capacity, the air handlers use 12 fans (six supply and six return), which are driven by motors controlled by energy-efficient variable-frequency drives. The system used MERV (minimum efficiency reporting value) 8 pre-filters with synthetic non-woven filter media made of continuous, hydrophobic fibers and MERV 14 rigid-box-style final filters made of fiber-glass filter media.

“As an improvement, we suggested that less-restrictive, higher-capacity final filters would provide advantages in terms of lower energy costs and longer service life,” Orlando said. “And by going to a higher MERV, we would increase the filter's ability to remove airborne particles, thus achieving the bank's IAQ goals.”

FROM BOX TO BAG

With overall efficiency in two-stage filtration systems primarily determined by the final filter, Orlando and his team decided to keep the MERV 8 pre-filters and upgrade the final filters to MERV 15.

“The MERV 8 pre-filters represented a good match to the proposed upgrade to the MERV 15 final filters, providing low resistance, excellent initial efficiency, sustained efficiency over time, and high dust-holding capacity for optimal performance and energy-cost savings,” Orlando said. “So, upgrading the pre-filter to a MERV 11 would be considered overkill with a MERV 15 final filter.”

Moving from a MERV 14 to a MERV 15 final filter involved more than a desire to increase particle-capture efficiency at submicron levels. First, the upgrade necessitated a move from a 24-in.-by-24-in.-by-12-in. rigid-box-style filter to a 24-in.-by-24-in.-by-22-in. bag filter.

Using 64 sq ft of media to the box filters' 54, the bag filters cost less per square foot of media. And with a longer service life — up to two years to the box filters' one — they have made filter changeout easier and less costly. The box filters came one to a package, while the bag filters come four, reducing installation, labor, and disposal costs.

“We are always evaluating our customers' systems to find ways to boost efficiency while lowering costs,” Orlando said. “In the case of the 1st National Bank of Arizona, we saw that they were paying for filter changes and labor they didn't have to.”

The media's structured density gradient helps improve energy efficiency and provides a solid mechanical foundation. An electret charge, coupled with an advanced mechanical structure, helps the media achieve a high initial efficiency, which it maintains over the useful life of a filter. The media is designed to optimize the balance between efficiency and pressure drop, while providing a high dust-holding capacity for long life.

The new filter media reduced airflow restriction from 0.65 in. to 0.48 in. at 500 fpm. With the variable-air-volume-system motor needing to overcome less resistance to deliver required airflow, energy savings are estimated to be approximately 10 percent.

“It's important to understand that the long-term cost of energy used by filters far outweighs the initial cost of the filter itself,” Dave Matela, CAFS, of Kimberly-Clark Filtration Products explained. “The lower the filter's resistance, the lower the energy consumption will be.”

Orlando added: “You know the price of something the day you buy it, while you know the cost of something the day you throw it away.”

With its low pressure drop and high particle-capture efficiencies, the synthetic filter media allowed 1st National Bank of Arizona to improve IAQ and reduce electricity costs simultaneously, a “seemingly contradictory concept,” Orlando concluded.